This invention relates to a thin film transistor (hereinafter referred to as "TFT") used for driving a liquid crystal panel or the like.
TFTs not having a light-shielding film such as shown in FIG. 2 with gate, source and drain electrodes 9, 10, 11 and TFTs having a light-shielding film are known in the art. In TFTs not having a light-shielding film, the thickness of an amorphous semiconductor is reduced down to about 500 .ANG. in order to reduce optical leakage current. According to this method, however, the optical leakage current can be reduced down to about 1.0.times.10.sup.-9 A. In conventional TFTs having a light-shielding film, on the other hand, the light-shielding film consists of an amorphous insulating film using germanium as its principal component. Therefore, the fabrication process of the light-shielding film is complicated and moreover, germane or monosilane as the starting gas is toxic to a human body.